In general, rotation speed of an engine for driving a working machine, such as a small-size versatile engine, is controlled to a rotation speed suitable for a load by opening control of a carburetor by a governor mechanism. There has been known the governor mechanism which moves a link mechanism by a centrifugal force corresponding to an engine rotation speed and transmits movement of the link mechanism to a throttle valve to perform throttle opening control. An engine used as the power source of a handheld mowing machine or blower is used at a relatively high rotation speed. Therefore, the conventional governor mechanism is hard to obtain a stable controlled effect and a working machine is required to be made smaller and more lightweight. Because of such situations, the engine is not provided with the governor mechanism in many cases.
In the engine which does not have the governor mechanism, the ignition timing of an ignition device is almost constant regardless of the change in the engine rotation speed and the engine rotation speed is the function of the throttle opening of the carburetor. The operator can perform variable control by the throttle opening adjustment operation. The throttle opening is maintained at a predetermined value, thereby maintaining the engine rotation speed at an almost constant value.
On the other hand, like a digital CDI, the ignition device of the engine is microcomputer-controlled so that the relation between the engine rotation speed and the ignition timing can be arbitrarily set. Using this, the ignition device has recently had appropriate ignition advance characteristics (as an example, see Japanese Patent Application Laid-Open No. 2005-163616).
[Patent Document 1] Japanese Patent Application Laid-Open No. 2005-163616